Electric valve converting system and control circuit therefor



p 1940- E. F. w. ALEXANDERSON 2,215,313

ELECTRIC VALVE CONVERTING SYSTEM AND CONTROL CIRCUIT THEREFOR FiledSept.- 29, 1959 Ernst F. W Al exanderson,

is Attorneg.

Patented Sept. 17, 1940 UNITED STATES PATENT OFFICE Ernst F. W.Alexanderson, Schenectady, N. Y.,

assignor to General Electric Company, a corporation of New YorkApplication September 29, 1939, Serial No. 297,123

7 Claims.

My invention relates to electric valve converting systems adapted totransmit energy between alternating current circuits of the same ordifferent frequencies, and more particularly to a control circuit forsuch systems.

Heretofore there have been devised various types of converting apparatusfor transmitting energy between alternating current circuits of the sameor different frequencies. Coincidently, there have been developednumerous arrangements for controlling the systems to effect the desiredoperation of the electric valve systems. Many of the control orexcitation circuits for the main or power electric valves have involvedapparatus complicated in arrangement and intricate in operation. In sucharrangements it has been found preferable to use electric valve means ofthe gaseous type for the power valves because of the relatively largeamounts of energy that may be handled at ordinary operating voltages. Inthe electric valve converting systems of the prior art it has been founddesirable to control the electric discharge valves in response to anumber of different electrical conditions to obtain the desired periodicenergy transfer. Generally the prior art arrangements involve the use ofauxiliary equipment of inordinate proportions to obtain the periodicenergization of the associated main electric valve means, especiallywhere a single control electrode is used for each electric dischargevalve. In order to eliminate the complicated excitation circuits and thelarge amount of auxiliary equipment necessary to operate the electricvalve apparatus, electric discharge valves have been used having twoseparate control electrodes each of which is energized in accordancewith a different electrical condition. Such a system has been describedand broadly claimed in my United States Letters Patent No. 2,122,271,granted June 28-, 1938. However, it would often be desirable to useelectric discharge valves having a single electrode without requiringthe complicated excitation circuits of the prior art but rather usingcontrol circuits which would be simple in arrangement and operation andwhich would assure certain and reliable performance.

It it an object of my invention, therefore, to provide an improvedcontrol circuit for electric valve converting systems adapted totransmit energy from an alternating current supply circuit to a loadcircuit which obviates the above mentioned undesirable features of theprior art arrangements and which is simple and reliable in operation.

It is another object of my invention to provide by means of improved andsimplified control apparatus.

In accordance with the illustrated embodiment of my invention I providean electric valve converting apparatus and excitation circuit thereforfor transmitting energy between alternating current circuits of the sameor different frequencies. The single control electrodes of the pluralityof electric discharge valves utilized in the electric valve convertingapparatus are arranged to be energized in accordance with a plurality ofcontrol potentials each responsive to a different electrical condition.A positive biasing means is connected in the grid to cathode circuit ofthe electric discharge valves tending to render the valves conductive,but a counteracting voltage appearing across a resistor in series withthe positive biasing means nullifies the effect of said positive biasingmeans except at predetermined periodic intervals when it is desired thatcertain valves are to become conductive. This counteracting voltage isresponsive to a plurality of different electrical conditions of saidsupply and load circuits, and until these electrical conditions are in acertain definite relationship the positive potential biasing meanscannot render the electric discharge valves conductive.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims. My inventionitself, however, will best be understood by reference to the followingdescription taken in connection with the accompanying drawing in whichthe single figure thereof diagrammatically represents an embodiment ofmy invention.

Referring now to the single figure of the drawing, I have illustratedtherein an electric valve converting apparatus for transmitting energybetween alternating current circuits l0 and II which may be of the sameor different frequencies, and one of the frequencies may even bevariable. Since my invention is equally applicable to the many differenttypes of electric valve converting apparatus known to those skilled inthe art, for simplicity of disclosure and explanation I have illustratedmy invention as applied to a frequency changing apparatusutilizing aminimum number of electric discharge valves for transmitting energybetween alternat ing current circuits I and II. rent circuit I0 isillustrated as a three-phase circuit although only a single phaseelectric valve converting system is connected thereto while alternatingcurrent circuit II is illustrated as a single phase circuit, but it willbe understood that the number of phases of alternating current circuitsIn and II is not critical as far as this invention is concerned. Theelectric valve converting apparatus interconnecting circuits I0 and IIwhich will be hereinafter termed load and supply circuits, respectively,comprises a transformer I2 and a plurality of electric discharge valvesI3, I4, I5, I8. Transformer I2 is provided with a primary winding I!connected across one phase of alternating current supply circuit I0 anda secondary winding I8 the terminals of which are connected to one ofthe electrodes of the plurality of electric discharge valves I3--I6,respectively. Each of the electric discharge valves I3IB is providedwith an anode I9, a cathode 20 and a control electrode or grid 2| andmay be any of the types of electric valves known to those skilled in theart, although I prefer to use valves of the vapor electric typecontaining an ionizable medium. The electric discharge valves areillustrated as being of the type comprising a single set of electrodesmounted in an envelope but it is to be understood that multi-anode,single cathode valves could be utilized in certain cases. Electricdischarge valves I3 and I4 have their anodes I 9 connected to theterminals of secondary winding I8 of transformer I2 and are arranged inthe form of a biphase rectifier for periodically transmitting apotential of one polarity to alternating current circuit II. Electricdischarge valves I and IS, on the other hand, have their cathodes 20connected to the terminals of secondary winding I8 of transformer I2 andare also arranged as a biphase rectifier so as to periodically transmita potential of the opposite polarity to alternating current load circuitII. A reactor 22 having terminals 23 and 24 respectively, and a midtap25, has its terminal 23 connected to the cathodes 20 of electricdischarge valves I3 and I4, while its terminal 24 is connected to theanodes I9 of electric discharge valves I5 and I6, respectively. It willbe obvious that regardless of whether energy is being transmitted byelectric discharge valves I3 and I4 or I5 and I6, current will fiowthrough a portion of reactor 22 wound on a single core 26 so as toproduce flux in only a single direction in the core 26 thereof. Since itis not necessary to build up flux first in one direction and then in theother with reversal of energy flow, reactor 22, therefore, presentslittle or no impedance to the normal energy flow between alternatingcurrent circuits I9 and II although a very high impedance is afforded toany short circuit or cross currents between electric discharge valvesI3, I4 and I5, I6.

In order to control the conductivity of electric discharge valves I3l6in accordance with a plurality of different electrical conditions, eachof the control electrodes or grids 2| is provided with an excitationcircuit 21, 28, 29 and 30, respectively. These excitation circuits2I--3ll include a positive biasing means illustrated as Alternatingcurbattery 3| connected in series with a resistor 32 in each of thegridto cathode circuits of electric discharge valves I3-I6,respectively. The positive biasing means 3| continuously tends to renderelectric discharge valves |3--IG conductive. However, excitationcircuits 2'|--30 also include a plurality of transformers 33 and 34having their secondary windings 35 and 35 each connected in series witha unilaterally conductive device 31 and 38, respectively. Each of thesecondary windings 35 and 36 and the serially connected unilaterallyconductive devices are connected in parallel with one another but inseries with the resistor 32. Transformer 33 is provided with a primarywinding 39 while transformer 34 is provided with a primary winding 40.The primary winding 39 of transformer 33 is arranged to be energizedfrom a source of primary frequency and is illustrated as being energizedby an alternating potential of the frequency of alternating currentcircuit I0 through rotary phase shifting transformer 4| and controltransformer 42. The primary winding 40 of transformer 34, on the otherhand, is arranged to be energized from a source of secondary frequencyand is illustrated as being energized by an alternating potentialobtained from alternating current circuit I I through transformer 43. Ifthe control potentials of primary frequency impressed on secondarywindings 35 of transformers 33 are such as to cause current to flow in adirection opposite to the direction of the arrow on the drawing, whichwill be referred to as negative potentials hereinafter, unilaterallyconductive devices 31 will allow current to flow through battery 3| andresistor 32 in such a direction as to produce a potential drop acrossresistor 32 and cause a negative potential to appear on controlelectrode 2| which overcomes the positive bias of biasing means 3|thereby maintaining the associated electric discharge valvenonconductive. The same will also be true if a negative potentialappearsacross the secondary winding 35 of transformer 34. Therefore, aslong as either one or both of the potentials of the secondary windings35 and 33 of transformers 33 and 34 are negative the associated electricdischarge valve will be maintained in a nonconductive condition byvirtue of the negative bias appearing across resistor 32. However, ifboth of the potentials of the secondary windings 35 and 36 oftransformers 33 and 34, respectively, are positive (e. g. such as totend to cause currents to flow in the direction of the arrows shown inthe drawing) unilaterally conductive devices 31 and 38 will prevent anycurrent from flowing through resistor 32 and therefore the positive biasof biasing means I is impressed upon the control electrode 2| of theassociated electric discharge valve rendering such electric dischargevalve conductive. It will be observed that the control alternatingpotential obtained from the source of primary frequency I 0 andimpressed on excitation circuits 21 and 28 are displaced in phase by 180electrical degrees with respect to the potential of alternating currentcircuit I II. However, the control potentials obtained from the sourceof secondary frequency II and impressed on excitation circuits 2! and 28are in phase with one another and 180 degrees displaced in phase withrespect to the control potentials from alternating current circuit llimpressed on excitation circuits 29 and 30, respectively,

The operation of the electric valve converting apparatus described abovewill be well understood by those skilled in the art and only a briefdescription will follow. Assuming, for example, that alternating currentcircuit I is the higher frequency circuit which alternating currentcircuit I I is the lower frequency circuit, then electric dischargevalves I3 and I4 will be rendered alternately conductive at thefrequency of the alternating current circuit I0 so as to produce a halfcycle of the alternating potential of load circuit II, after which thesevalves will be rendered nonconductive and electric discharge valves l5and I6 will be alternately rendered conductive at the frequency ofalternating current circuit I0 so as to produce a half cycle of oppositepolarity at alternating current circuit II. Groups of valves I3-I4andIS-Iii are rendered alternately conductive and nonconductive at thefrequency of alternating current circuit II. At one particular instantthe control potentials from the source of secondary frequency IIimpressed on secondary windings 36 of transformer 34in excitationcircuits 2'! and 28 are positive so that unilaterally conductive devices38 allow substantially no current to flow through resistors 32associated with electric discharge valves I3 and I4. At this sameinstant the control potentials from the source of secondary frequency IIimpressed on excitation circuits 29 and 30 are negative so that currentsflow through resistors 32 of excitation circuits 29 and 30 and electricdischarge valves I5 and I6 are rendered nonconductive. If now a positivepotential is also impressed on secondary Winding of transformer 33associated with excitation circuit 21 current will flow through resistor32 of excitation circuit 2! and electric discharge valve I3 is renderedconductive. It is assumed that the anode cathode voltage of electricdischarge valve I3 at this instant is in such a direction as to causecurrent to flow through electric discharge valve I3 through upperportion of reactor 22 to one side. of alternating current circuit II. Atthis same instant the potential across secondary winding 35 oftransformer 33 of excitation circuit 28 is negative so that currentflows through resistor 32 associated with electric discharge valve I4,overcoming the positive bias of battery 3I thereby maintaining electricdischarge valve I4 nonconductive. One hundred eighty electrical degreeslater with respect to alternating current circuit Ill electric dischargevalve I4 is rendered conductive and current is commutated from electricdischarge valve I3 to electric discharge valve I4. Thus electricdischarge valves I3 and I4 are rendered alternately conductive andnonconductive until the potential of alternating current circuit IIreverses, thereby causing a negative potential to be impressed onsecondary windings 36 of transformers 34 associated with excitationcircuits 21 and 28, respectively, and a positive potential to beimpressed on secondary windings 36 of transformers 34 associated withexcitation circuits 29 and 30, respectively. Thereafter electricdischarge valves I5 and I6 are alternately rendered conductive andnonconductive at the frequency of the source of primary frequency III inthe same manner as described in connection with electric dischargevalves I3 and I4, and the next half cycle of the alternating potentialof alternating current circuit II is produced. Therefore, electricdischarge valves I3 and I4 are controlled as a biphase rectifier toproduce a half cycle of one polarity on alternating current circuit IIand the electric discharge valves I5 and I6 are controlled as a biphaserectifier to produce the next half cycle of opposite polarity onalternating current circuit II.

While I have described what I at present consider the preferredembodiment of my invention, 5 it will be obvious to those skilled in theart that various changes and modifications may be made without departingfrom my invention, and I, therefore, aim in the appended claims to coverall such changes and modifications as fall within the true spirit andscope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In combination, an alternating current circuit of primary frequency,an alternating current circuit of secondary frequency, a plurality ofelectric discharge valves interconnecting said circuits, a controlelectrode and excitation circuit for each of said electric dischargevalves comprising a biasing means continuously tending to render saidelectric discharge valves conductive, and means for deriving a controlpotential at each of said frequencies of such magnitude that either ofsaid control potentials periodically overcomes said biasing means torender said electric discharge valves nonconductive in a predeterminedsequence.

2. In combination, a supply circuit, a load circuit, an electrictranslating apparatus interconnecting said circuits comprising aplurality of electric valve means, each provided with a controlelectrode and an excitation circuit comprising means for impressing apositive bias potential on each of said control electrodes continuouslytending to render said electric discharge valves conductive, and meansresponsive toelectrical conditions of said supply and load circuits forovercoming said biasing means to render said electric valve meansnonconductive in a predetermined sequence.

3. In combination, an electric valve means having a control member andemploying an ionizable medium, a control system for energizing saidcontrol member comprising a plurality of sources of control potentialsconnected in parallel and each derived in response to a differentelectrical condition, means continuously tending to render said electricvalve means conductive, and means for periodically impressingunidirectional impulses of said control potentials on said controlmember, each of said control potentials being of sufficient magnitude toovercome said first mentioned means to render said electric valve meansnonconductive for predetermined intervals.

4. In combination, an alternating current eircuit of one frequency, asecond alternating current circuit, an electric translating apparatusinterconnecting said circuits and comprising a plurality of electricvalve means, each provided with a control electrode and associatedexcitation circuit, said excitation circuit comprising a resistanceserially connected with said control electrode, means responsive to anelectrical condition of said first mentioned alternating current circuitfor producing a potential across said resistor, means responsive to anelectrical condition of said second alternating current circuit forproducing a potential across said resistor, unilaterally conductivedevices for determining the polarity of the potential produced acrosssaid resistor by both said responsive means and a positive biasing meansfor rendering said associated electric discharge valve conductive whenthere is substantially no potential across said resistor.

5, In combination, an electric valve means hav- 75 ing a control member,a control circuit for energizing said control member comprising aplurality of sources of control potential, a resistance seriallyconnected with said control member, means responsive to one of saidsources of control potential for producing a potential across saidresistor, means responsive to another of said sources of controlpotential for producing a potential across said resistor, unilaterallyconductive devices for determining the polarity of the potentialproduced across said resistor by said sources of control potential, anda positive biasing means for rendering said electric valve meansconductive when there is substantially no potential across saidresistor.

6. In'combination, an alternating current circuit of one frequency, analternating current circuit of another frequency, an electric valvefrequency changer interconnecting said circuits and including aplurality of electric discharge valves, an excitation circuit for eachof said valves comprising a source of potential tending to maintain saidvalves continuously in one state of conductivity, means for deriving acontrol potential from each of said alternating current circuits andimpressing half waves of one polarity of each of said control potentialson said excitation circuit, the magnitude of each of said controlpotentials being suflicient to overcome said biasing means to changesaid valves to the opposite state of conductivity periodically.

7. In combination, an alternating current circuit of one frequency, analternating current circuit of a second frequency, an electric valvefrequency changer interconnecting said circuits and comprising aplurality of groups of valves, an excitation circuit for rendering thevalves of one of said groups alternately conductive and nonconductive atthe frequency of one of said circuits and for rendering said groupsalternately conductive and nonconductive at the frequency of the otherof said circuits comprising means for biasing all of said valves to onestate of conductivity, means for deriving a control potential from eachof said circuits, and means for impressing on said excitation circuithalf waves of each of said control potentials of a polarity opposite tosaid biasing potential to reverse the state of conductivity of saidvalves, said control potentials each having a magnitude suificient toovercome the effect of said biasing potential.

ERNST F. W. ALEXANDERSON.

